At least as measured in spending on campaign advertising, Minnesota has remained a backwater in the presidential race.

While more than $50 million -- a record -- has been spent on presidential campaign ads nationwide during the past two months, John McCain and Barack Obama have spent just $645,000, combined, in Minnesota, according to the University of Wisconsin Advertising Project.

That's the least, by far, spent by the campaigns in 14 battleground states, according to the project, which tracks political advertising.

And while both campaigns have sent strong signals that they believe they can win Minnesota in November, the relative paltriness of their spending here suggests that for now it remains strictly a second-tier battleground.

For example, a combined $3.1 million has been poured into Wisconsin by Obama, McCain and the Republican National Committee.

The spending patterns indicate that the true battlegrounds so far have been in Ohio, Michigan, Pennsylvania and Wisconsin. Spending in those states totaled nearly $26 million between June 3, when the primary season ended, and July 26, the advertising project found. Ads run in 17 other states totaled about the same amount.

And despite Obama's massive fundraising lead over McCain, that hasn't translated into a comparable advantage in advertising. McCain's spending has outstripped Obama's in all of the battleground states, except North Dakota, Virginia and New Hampshire.

In Minnesota, for example, McCain has paid for $575,000 worth of ads to Obama's $70,000, and the Republican went on the air almost two weeks earlier than the Democrat.

But in total advertising nationwide, Obama is well ahead of McCain. Obama's campaign has spent more than $27 million, while McCain's has spent more than $21 million. That paid for more than 100,000 commercial airings.

One decided McCain advantage, one that he is expected to retain, is financial support from his party. The Republican National Committee spent $3.6 million, airing some 4,000 ads. The Democratic National Committee hasn't bought a single commercial.